1. Field of the Invention
The present invention has to do with apparatus and methods for performing osteotomies and drilling holes in bones. More specifically, the invention relates to apparatus and methods for harvesting bone from the operating site during the osteotomy or bone drilling procedure so that it can be used to augment the bone fusion process.
2. The Related Art
Osteotomies are routinely performed for surgical access or to divide (and reposition) a bone for the correction of a skeletal deformity. Holes may be drilled in bones for various reasons to accommodate screws, pins and various other implantable devices and materials or to take a bone sample for analysis.
One of the more common examples of an osteotomy for surgical access is a craniotomy. In this procedure, the surgeon removes a significant portion of the patient's skull (termed a craniotomy flap, a cranial flap, a skull flap or bone flap) for access to the brain. The removed section of the skull is set aside in a sterile field and at the end of surgery, it is returned to its original position and affixed to the native skull, typically with plates and screws. The intent of the surgeon is to restore the patient's skull to its original contour and to provide physical protection for the brain. The ideal outcome would be complete fusion of the craniotomy flap to the native skull, leaving no long term bony deficit or weakness. In addition, many surgeons would prefer there to be minimal foreign bodies remaining and no imaging artifacts postoperatively. Unfortunately this is difficult to accomplish with the current surgical techniques.
The surgical instrument used to cut the craniotomy (a craniotome) utilizes a rotating cutter approximately 2 mm in diameter. The bone that is removed by this instrument is lost during surgery and as a result, when the cranial flap is returned to its original position, there is a gap around the entire periphery which corresponds to the diameter of the cutter. This gap creates a number of problems. The most obvious deficiency is that bone-to-bone contact, essential for achieving bony fusion, is impossible around the periphery of the cranial flap. This continuous gap (or kerf) creates a surgical “dead space” which is never desirable, it also allows soft tissue (the scalp and dura) to intrude into this space and inhibit bony healing. The step-off between the skull and cranial flap also may result in a cosmetic deformity for the patient. To combat these problems, surgeons use one or more strategies which have their own shortcomings. For example, the surgeon may choose to bias the cranial flap toward one side of the craniotomy. This produces bone-to-bone contact in a local area but increases the gap elsewhere around the periphery.
The surgeon may also elect to fill the gap between the skull and skull flap with a material which will encourage bony fusion. These fill materials can be autologous, allograft, or artificial. Autologous bone grafts are harvested directly from the patient and are the “gold standard,” since they are inherently biocompatible, osteoconductive, osteoinductive, and osteogenic. Harvesting autologous bone is currently carried out by taking bone from a part of the patient's body other than the surgical site. This results in additional surgical time and the additional (surgical) harvest has its own attendant risk of complications such as donor site pain and morbidity. Allografts, derived from donor (cadaver) tissues, are only osteoconductive, and they involve considerable cost, pose the risk of disease transmission and are objectionable to certain religious groups. Artificial materials such as alloplastic bone cement are another alternative. These bone cements are almost always used in conjunction with plates and screws. The drawbacks to this approach include substantial additional cost, risk of infection and no certainty that the bone cement will ever remodel into actual bone.
While this problem is illustrated with a craniotomy example, it occurs whenever an osteotomy is created strictly for surgical access and the bones must be returned to their original positions in order to prevent a postoperative deformity or a functional problem. In the skull alone, this problem exists in skull base surgery, craniofacial tumor surgery and mandibular osteotomies for oncologic resection. At the conclusion of all these procedures, the surgical goal is to restore the original bony anatomy. This precludes achieving bone-to-bone contact of the severed ends since they must remain separated by the width of the blade (or cutter) used for the osteotomy.
Perforations (or holes) are routinely created in bones for surgical access and other reasons. These perforations may be performed for biopsy purposes, to create access for minimally invasive surgery or as the prelude to an osteotomy. An example of the latter is the burr hole that is initially created in the skull which allows the craniotome to be inserted for completion of the craniotomy. In these cases, it is desirable to close the perforation, preferably in a manner which restores the bone to its original condition. Additionally, holes are routinely drilled into bone as a step in preparation for orthopedic screw or pin insertion. Most of these cases would also benefit from the availability of autologous bone graft.
When osteotomies are used to divide a bone so that it may be repositioned to correct a surgical deformity, a different problem exists. In many cases, bone graft material is needed to fill the gaps created as the bones are repositioned and severed bony ends move relative to each other. This is obviously the case where a gap is intentionally created, such as an osteotomy to elevate a collapsed tibial plateau. It also may occur when the intent of the osteotomy is to decrease the bone volume. In these surgeries it is not uncommon for the contours of the bony ends to be slightly mismatched and in these cases the surgeon may elect to augment the fusion with additional bone graft material. As previously discussed, allograft bone, autogenous bone or alloplastic materials may all be used in such situations, each with their related problems.
In all these procedures where an osteotomy (or perforation) is necessary, a common problem exists: bone is removed by the osteotomy or drilling instrument and at the conclusion of surgery, additional bone is required to complete the reconstruction.
The current surgical practice is to manually irrigate the bone as it is cut and also to manually suction off the resulting solids and liquids into the operating room's non-sterile vacuum system. These activities are performed concurrently by other operating room personnel while the surgeon operates the osteotomy instrument. Some of the shortcomings of these practices are detailed in the following text which is excerpted from the USC Neurosurgery website. (http://uscneurosurgery.com/infonet/ecrani/instruments.htm).
Irrigation                With even optimal illumination and magnification and organization of his field, the surgeon is still incapacitated by obscuring blood, cloudy irrigation fluid, or other debris. Efficient intracranial surgery requires keeping the operative field clear of physical and visual obstacles by diligent irrigation, attentive aspiration, and meticulous hemostasis.        Irrigation and aspiration are complimentary aspects of surgical field maintenance. The irrigating-aspirating assistant must concentrate on following the movements of the surgeon's hands visually and with irrigant and suction. Areas of surgical interest are most safely addressed at the time of maximal cleanliness; immediately after they have been washed clean and aspirated dry.        Irrigant should be squirted onto the field under enough pressure to displace blood, but if the bulb is squeezed too hard and fluid issues under too much pressure, fluid from the bulb will be reflected back against the stream because it cannot dissipate fast enough, with the consequence that a splashing of mixed blood-irrigant fluid ends up in the surgeon's face and widely scattered across the field. Better control of the stream from the irrigation fluid bulb is achieved by manipulating it with the dominant hand.        The primarily aqueous solution used for surgical irrigation not only dilutes the blood but pushes it ahead of the irrigant stream. This washing force is greatest at the tip of a irrigation bulb where the irrigant fluid pressure is maximal.        
Suction                Blood accumulates with irrigation fluid in dependent portions of the field as it escapes and is washed from lacerated vessels. The bloody fluid then interferes with the working of the electrocautery devices used to stop further bleeding from the openings in the vessels. To this is added the problem of blood's opacity, so that even in small quantities as even a thin layer, it obscures the surgical field.        Suction is a maintenance activity, keeping the operative field clear of debris, blood, or smoke that can obstruct visualization. Whenever possible the suction attachment should be held in the non-dominant hand.        Surgical field suction instrumentation attaches to the same suction canisters which provide suction for anesthesia. Distally non-sterile, proximally sterile tubing connects the suction device to the distal end of the metal suction handle and tip. The proximal end of the metal sucker connects to the suction tubing.        
The importance and difficulty of performing simultaneous irrigation and suction in concert with the surgeon's movements are detailed above. Later in the text they discuss the importance of irrigation when cutting the bone:                Bone is perforated and/or cut in the course of any intracranial trauma surgery. Irrigation accomplishes two purposes in the setting of drilling bone. First, it cools down the bone. This is important in terms of the mechanics of bone cutting. The bits cut more effectively through cooler bone and in the absence of bone dust that can clog its rotations.        
These comments are directed toward neurosurgical craniotomies but the same principles apply to all osteotomies and perforations. Proper irrigation not only improves the efficiency of the cutting instrument, it also prevents thermal necrosis of the bone which can later retard the healing process. This principle takes on even greater importance when one intends to collect the bone particles generated during the cutting process and reuse them in surgery. Irrigation has traditionally been conducted using a liquid. But according to the present invention we can irrigate with a liquid or compressed gas source or a combination of liquid and a compressed gas source. The compressed gas can be chilled if required and also can be intermixed with a fluid (e.g., saline).
Up until now, a reliable and essentially free source of autogenous bone has been overlooked by the surgical community. Manufacturers of surgical cutting instruments have incorporated irrigation on some instruments but none have ever proposed taking the concept one step further—collecting the bone particulate in a sterile fashion for later use in the bony reconstructive phase of the surgery.
We have now developed apparatus and methods for sterilely collecting and containing the particulate bone created during osteotomy and bone drilling procedures. The apparatus and methods also enable more controlled irrigation of the bone as it is cut or drilled and a reduction in the amount of patient bone that is scattered or aerosolized during surgery.
The terms particulate bone, bone particulate and bone particles are used interchangeably in this patent and all are intended to have the same meaning.